Graft copolymers of polystyrene and polyisobutylene

ABSTRACT

Copolymers useful as shear stable viscosity index improvers, are graft copolymers of polyisobutylene onto a polystyrene backbone. The copolymers are formed by the grafting of polyisobutylene onto the polystyrene backbone using Friedel Crafts catalysts.

United States Patent [191 Forbes et a1.

[ 1 July 8,1975

[ GRAFT COPOLYMERS OF POLYSTYRENE AND POLYISOBUTYLENE [75] Inventors: Eric Simon Forbes, Lightwater; Ian

Grieg Meldrum, Little Sandhurst near Camberley, both of England [73] Assignee: The British Petroleum Company Limited, London, England [22] Filed: Nov. 10, 1972 [21] Appl. No.: 305,228

[30] Foreign Application Priority Data Nov. 16, 1971 United Kingdom 53079/71 [52] US. Cl. 260/896; 260/886; 252/59 [51] Int. Cl. C08f 29/12 [58] Field of Search 260/896, 886, 878

[56] References Cited FOREIGN PATENTS OR APPLICATIONS 640,566 7/1950 United Kingdom 235,262 10/1957 Australia 260/878 640,567 7/ 1950 United Kingdom 575,571 5/1959 Canada 260/878 Primary Examiner-John C. Bleutge Assistant Examiner-C. J. Seccuro Attorney, Agent, or Firm-Morgan, Finnegan, Durham & Pine 2 Claims, No Drawings GRAFT COPOLYMERS OF POLYSTYRENE AND POLYISOBUTYLENE This invention relates to polymers and a method for their preparation, more particularly it relates to copylymers of polystyrene and polyisobutylene and to methods of their preparation.

Polystyrene and polyisobutylene copolymers of the present invention have a wide range of uses in the manufacture of articles, packaging materials and certain of the copolymers are useful as viscosity index improvers in lubricating oils.

The viscosity index of a lubricating oil is a measure of the change of viscosity of the lubricating oil with change of temperature. The higher the viscosity index of the oil, the less decrease in viscosity with increase in temperature of the oil. The viscosity index of an oil can be calculated by ASTM method D2270 (IP 226/68).

It is known from United Kingdom Pat. Nos. 640,567 and 681,428 to alkylate polystyrene of molecular weight 20,000 to 80,000 (Staudinger) with a propylene polymer to form an alkylated polystyrene with viscosity index improving properties. The polypropylenes described are formed by polymerising propylene using phosphoric acid as a catalyst and the polymers have a boiling point of 55C to 235C, and are mixtures of dimers, trimers and tetramers of propylene. These patents also show that polystyrenes of higher molecular weight are readily shared and are consequently little use as viscosity index improvers.

United Kingdom Pat. No. 640,566 describes the alkylation of a polystyrene of molecular weight above 3000 with an alkyl halide or dimer, trimer or tetramer of propylene or butylene in the presence of an organic nitro-compound. This patent states that for viscosity temperature improvers of mineral oils the polystyrene in the copolymer should have a molecular weight of less than 60,000, and describes a process whereby a polystyrene of molecular weight above 60,000 can have its molecular weight reduced.

We have surprisingly found that graft copolymers of polystyrene and polyisobutylene in which higher molecular weight polystyrenes and polyisobutylenes are used have excellent viscosity modifying properties and some are very shear stable.

According to the invention there is provided a graft copolymer of polystyrene and a polyisobutylene comprising a polystyrene back-bone of molecular weight 50,000 to 1,000,000 having joined thereto polyisobutylene groups of molecular weight 750 to 1,000,000, whereby each polyisobutylene group is attached to the polystyrene back-bone.

The molecular weight of the polystyrene back-bone is preferably 50,000 to 500,000, more preferably 80,000 to 450,000 and most preferably 80,000 to 3,000,000.

The molecular weight of the polyisobutylene groups is preferably 1,000 to 20,000 most preferably 2,500 to 10,000.

The amount of polyisobutylene in the copolymer is preferably -50% by weight, more preferably 40% wt., most preferably 2030% wt.

It is thought that the polyisobutylene groups are attached to the benzene nuclei of the polystyrene groups.

When the copolymers of the present invention are used in lubricating or other oils as viscosity index modifiers, the copolymer used should be soluble in the oil.

The solubility of the copolymer in the oil is affected by the molecular weight of the polystyrene, the molecular weight of the polyisobutylene, the ratio of polystyrene to polyisobutylene and the nature of the oil. Generally speaking it has been found that the copolymers formed from the lower molecular weight polyisobutylenes and higher molecular weight polystyrenes are most soluble in mineral oils.

The invention also provides a lubricating oil composition which comprises a lubricating oil having dissolved therein a graft copolymer of polystyrene and polyisobutylene as described above.

The lubricating oil composition preferably comprises 0.1 to 15% wt. of the graft copolymer, more preferably 0.5 to 10% wt.

As well as being used in lubricating oils the copolymer of the present invention can be used in hydraulic and other similar oils.

The graft copolymers of the present invention can be prepared by Friedel-Crafts catalysis of the reaction of polyisobutylene and polystyrene.

According to the invention there is provided a method of preparing graft copolymers of polystyrene and polyisobutylene which comprises to reacting a polystyrene of molecular weight 50,000 to 1,000,000 with a polyisobutylene of molecular weight 750 to 1,000,000 in the presence of a Friedel-Crafts catalyst.

The polystyrene preferably has a molecular weight of 50,000 to 3,600,000, more preferably 50,000 to 500,000 and most preferably 80,000 to 450,000.

The polyisobutylene preferably has a molecular weight of 750 to 50,000 more preferably 1,000 to 20,000 and most preferably 2,500 to 10,000.

The weight ratio of polystyrene to polyisobutylene is preferably 40:60 to :15 measured as to the amount in the final product, more preferably 60:40 to 80:20 and most preferably 80:20 to 70:30.

Friedel-Crafts catalysts are a well known range of catalysts, and Friedel-Crafts polymerisation and alkylation catalysts can be used. The preferred catalysts are aluminium chloride, boron trifluoride and stannic chloride.

The Friedel-Crafts catalyst is preferably present in an amount of 0.01 to 5%-wt. based on the total weight of the reaction mixture.

The reaction is preferably carried out in an inert solvent such as a chlorinated hydrocarbon, e.g. dichlorobenzene, 1,2-dichloroethane or trichloroethylene, a particularly preferred solvent is a mixture of 1,2- dichloroethane and tric'hloroethylene. Preferably there is also present in the reaction mixture an organic nitro compound e.g. a nitro-alkane such as nitro-propane or nitro-benzene. A preferred method of carrying out the invention is to dissolve the polystyrene in the solvent, add the Friedel-Crafts catalyst and organic nitro compound, and then add the polyisobutylene dissolved in more solvent. The reaction is preferably carried out with gentle warming e.g. to C to facilitate the reaction.

1f the copolymer is to be used as a viscosity index improver, a lubricating oil can be added to the reaction mixture before removal of the solvents, to that when the solvents are removed an oil concentrate is obtained.

In this specification and claims the molecular weight of the polystyrene is expressed as a weight average, and

3 the molecular weight of the polyisobutylene is expressed as a number average.

The invention will now be described with reference Table 10 Polystyrene M 270,000 Polyisobutylene M,, 2,400

to the following Examples. Approx Kinematic Viscosity (cSt) I EXAMPLE 1 Content 7: Before Shear After Shear 100F 210F vlE 100F 210F VIE Polystyrene (30g) of weight average molecular 62 54.60 8.61 145 46.71 7.34 131 weight 0080.000 was dissolved in 200 mls. ofa 2.1 m1x 48 5589 896 152 49.14 710 134 ture of trichloroethylene and l,2-d1chloroethane in a 7 45.94 735 130 43.29 6.74 120 stirred flask. A solution of 2g of AlCl in 30 mls 2- 10 3244- insoluble in Base Oil nitropropane was then added to the flask.

A polyisobutylene of number average molecular weight 2,400 (14 grms) was dissolved in 70 mls ofa 2:] Table 2a mixture of trichloroethylene and l,2-dichloroethane 5 and pumped in over a period of 0.5 hour. The reaction Polystyrene M,,. 80.000 Polyisobutylene M,, 6,100 temperature was maintained at 40 50C and the reif g Knematc vscosty (cSt) actlon completed m 2 hours- Content Before Shear After Shear The activity of the AlCl catalyst was then killed by 0 21 IE 100F 210F VlE the addltlon of d lute HCl. The aqueous layer was sepa- 37 4948 7'90 140 47.80 7455 34 rated and orgamc layer washed with water. The poly- 45 50.09 7.85 136 48.09 7.51 131 mer was precipitated by methanol, dissolved in toluene and reprecipitated to remove unreacted polyisobutylene. It was finally dried in a vacuum oven. The copoly- Table 2b mer formed consisted of a polystyrene back-bone having the polyisobutylene groups attached randomly to Polystyrene M,,. 180,000 Polyisobutylene M,, 6.100

Approx Kinematic Viscosity (cSt) the back bone C PIE (7 Before Shear After Shear ontent I EXAMPLE 2 100F 210F VlE 100F 210F VIE Example lflwas repeated using various polystyrenes 3O 45 6118 978 152 5662 823 140 and polylsobutylenes 1n differing amounts. 38 58.28 9.21 150 52.31 8.17 139 The polymers obtained were dissolved in a solvent SI 147 5149 refined mineral oil of viscosity at 100C of 32 centistokes and the viscosity at 210C of 5.29 centistokes, 35 to form a 2% solution. The viscosities of the solutions Table 2C at 100C and 210C were measured and the viscosity P l M 270 00 P l M 0 ystyrene ,0 o yisobutylene 6,100 index calculated by ASTM method D2270 to give the Approx Kinematic viscosny (CS0 VIE value. p13

The oil compositions obtained were sheared by the 40 Content 100F 2 32 5 VIE g VIE Diesel Injector Rig test, in this test 50 ml of the test oil is placed in a glass reservoir and is pumped through a 43 62.05 9.95 157 52.88 8.27 140 diesel in'ector and then into a receivin vessel at 3000 48 1031 154 5460 140 J g 57 69.46 10.80 159 53.49 8.27 138 ps1, this constitutes one cycle. The viscosities of the so- 74 62.94 9.88 153 49.47 7.68 132 6 o 37 74.47 12.75 184 52.95 8.43 145 lutions were agammeasured 100 C to 210 C and the 26 42.69 1008 248 4229 10.00 248 vlscoslty index again calculated.

The results are shown below in the Tables.

Table la Table 2d Polystyrene-M 80.000 Polyisobutylene-M, 2,400 Polystyrene n- 4304000 P y b yl n n 64100 Approx Kinematic Viscosity (cSt) pp Kmemanc Vlscoslly (CS!) 'PIB Before Shear After Shear FIB a o Content 74 Before Shear After Shear 7 Content 7: 100 F 210 F VIE 100 F -10 F VIE 100F zlOOF VIE 100F 210F VIE sheared at 80C Table 1b Table 3 Polystyrene-M. 180.000 Polyisobutylene-M,.= 2,400 Polystyrene M,,- 270,000 Polyisobutylene M,, 9,000

Approx Kinematic Viscosity (cSt) Approx Kinematic Viscosity (cSt) PlB Before Shear After Shear PlB Content 100F 210F VIE 100F 210F VIE Content 100F 210F VIE Hyvis 10,000 Copolymer Table 4 Polystyrene M 270.000 Polyisobutylene M,, 12.000

Approx Kinematic Viscosity (cSt) PlB Content 7: 100F 210F VIE Various commercially used polymeric viscosity index improvers were tested for shear stability at the same concentration as the viscosity index improvers of the invention, and the results are shown in the Table 5.

Before Shearing After Shearing Polymeric Viscosity Viscosity at Viscosity at VlE Viscosity at Viscosity at VIE lndex lmprover 100F 210F 100F 210F A 48.34 8.65 171 41.96 7.21 147 B 52.8 10.03 194 47.70 8.03 152 C 61.49 10.53 174 53.91 8.91 159 D 43.31 6.82 124 42.06 6.56 118 E 42.69 10.08 248 42.29 10.0 248 F 50.09 7.85 136 48.09 7.51 131 All the polymers were dissolved at 2% wt. concentration in the ase oil.

A is a polyalkyl methacrylatc of weight average molecular weight about 350,000. B is a pnlyulkyl mcthacrylatc of weight average molecular weight about 500,000 C is a polymcthacrylatc of weight average molecular weight above 400.000.

D is a polyisohutylenc of number average molecular weight about 30.000.

E is a polystyrenc/polyisobutylenc VI improver of 6 of Table 2c.

F is a polystyrenc/polyisobuutylene VI improver of 2 of Table 2a.

2. A graft copolymer as claimed in claim 1 which consists essentially of 80 to of a polystyrene of molecular weight 80,000 to 450,000 and 20 to 30% weight of a polyisobutylene of molecular weight 2,500 to 10,000. 

1. A GRAFT COPOLYMER OF POLYSTYRENE AND POLYISOBUTYLENE WHICH CONSISTS ESSENTIALLY OF 85 TO 40% WEIGHT OF A POLYSTYRENE OF WEIGHT AVERAGE MOLECULAR WEIGHT 50,000 TO 500, 000 AND 15 TO 60% WEIGHT OF A POLYISOBUTYLENE OF NUMBER AVERAGE MOLECULAR WEIGHT 2,500 TO 20,000, THE SAID GRAFT COPOLYMER BEING IN THE FORM OF A POLYSTYRENE BACK-BONE HAVING EACH POLYISOBUTYLENE GROUP ATTACHED THERETO AND PREPARED BY REACTING POLYSTYRENE AND POLYISOBUTYLENE.
 2. A graft copolymer as claimed in claim 1 which consists essentially of 80 to 70% of a polystyrene of molecular weight 80, 000 to 450,000 and 20 to 30% weight of a polyisobutylene of molecular weight 2,500 to 10,000. 